96 OF FERTILIZERS. 



CHAPTER XII. 



OF FERTILIZERS. 



321. The soil ought to contain all the elements neces 

 sary to the nourishment of plants. These have already 

 been spoken of in the chapter upon the various elementary 

 substances found in plants. They are : 1, oxygen ; 2, 

 carbon, in the state of carbonic acid ; 3, hydrogen ; 4, 

 nitrogen, in the shape of ammonia ; 5, silicon ; 6, sulphur, 

 and 7, phosphorus ; 8, chlorine, and 9, sodium, in the 

 shape of common salt; 10, calcium; 11, potassium; 12, 

 magnesium ; 13, iron ; 14, manganesium. It must also 

 contain 15, aluminum, as the basis of clay, and, though 

 in minute quantity, 16, fluorine ; and the water or the 

 soil must contain for certain marine plants, 17, iodine, 

 and 18, bromine. 



322. These, except the first four, atmospheric elements, 

 are always found in combination, as silicates, sulphates, 

 nitrates, phosphates, carbonates and fluates, of potash, 

 soda, lime, magnesia, iron, manganese and alumina, or 

 in other forms sometimes more complex. 



We know that these are all essential to plants, because 

 we find them all in the ashes of plants. 



If any one of these elements were absolutely wanting 

 in a soil, the plants to which that element was essential 

 could do little more than sprout there ; and if planted or 

 sown in such a soil, would starve to death. Plaster, for 

 example, is essential to clover ; and clover seed, sown in 

 a soil which contained no plaster, would not coino up. If 

 there were a very little plaster in the soil, the clover 

 might come up, but would not flourish. 



